Cam position measurement for embedded control VCT systems using non-ideal pulse-wheels for cam position measurement

ABSTRACT

In a VCT system having a phaser and pulse wheels on driving and driven shafts respectively in which the pulse wheels have known tooth distribution thereon, a device and method is used for adjusting values of a controller that controls the timing between the driving and driven shaft. Additional subroutines are performed with respect to the driving shaft tooth wheel and the driven shaft tooth wheel respectively. The known tooth distribution includes non-symmetric tooth distribution.

FIELD OF THE INVENTION

The invention pertains to the field of cam position measurement. Moreparticularly, the invention pertains to cam position measurement forembedded control VCT systems using non-ideal pulse-wheels for camposition measurement.

BACKGROUND OF THE INVENTION

United States published patent application, 2002/0050272 entitledCYLINDER IDENTIFYING SYSTEM FOR INTERNAL COMBUSTION ENGINE, teaches acylinder identifying system for an internal combustion engine capable ofestablishing a complicated cam signal pulse pattern without need forsetting specific periods for cylinder identification while enhancingcontrol performance by reducing a crank rotation angle required forcylinder identification. A cylinder identifying means (10) foridentifying discriminatively individual cylinders on the basis of acrank angle pulse signal (SGT) and a cam pulse signal (SGC) includes apulse signal number storage means (12) for counting for storage signalnumbers of specific pulses generated over a plurality of subperiodswhich are defined by dividing an ignition control period for each of theindividual cylinders into plural subperiods, and an information seriesstorage means (15) for storing information series each composed of acombination of the signal numbers generated during plural subperiods,respectively. The individual cylinders are identified on the basis ofthe information series.

United States published patent application, 2001/0011203, entitledENGINE CONTROL UNIT HAVING CYLINDER DETERMINATION FUNCTION, teaches acrank signal generated by a crank angle sensor has a front pulse missingportion and a back pulse missing portion in a pulse train of everypredetermined angle interval. The level of a cam signal generated by acam angle sensor becomes different in the pulse missing portion of thecrank signal. A level different from that in the pulse missing portioncontinues for a period of predetermined angles before the pulse missingportion. A microcomputer determines each of the front and back pulsemissing portions in the crank signal on the basis of the level of thecam signal in the pulse missing portion of the crank signal in twocycles of the rotation of a crankshaft of the engine and the duration ofa different level before the pulse missing portion.

U.S. Pat. No. 6,498,979, entitled ENGINE CONTROL UNIT HAVING CYLINDERDETERMINATION FUNCTION, teaches a crank signal generated by a crankangle sensor has a front pulse missing portion and a back pulse missingportion in a pulse train of every predetermined angle interval. Thelevel of a cam signal generated by a cam angle sensor becomes differentin the pulse missing portion of the crank signal. A level different fromthat in the pulse missing portion continues for a period ofpredetermined angles before the pulse missing portion. A microcomputerdetermines each of the front and back pulse missing portions in thecrank signal on the basis of the level of the cam signal in the pulsemissing portion of the crank signal in two cycles of the rotation of acrankshaft of the engine and the duration of a different level beforethe pulse missing portion.

U.S. Pat. No. 5,736,633, entitled METHOD AND SYSTEM FOR DECODING OFVCT/CID SENSOR WHEEL, teaches a Battery charging system for vehicles,uses fixed chargers on roadsides. “Translocator” on vehicle triggerspower transmission (and keeps track of cost of energy). When chargerdetects translocator signal, it steers microwave or laser energy toreceiver on vehicle. Does not explain how “translocator” works otherthan details of metering and payment (see col 5 lines 35-65), but fromdescription it appears that translocator continually transmits and thebase station somehow triangulates (“locks onto” in the words of thepatent) the translocator signal.

U.S. Pat. No. 4,953,531, entitled CRANK ANGLE DETECTOR FOR AN ENGINE,teaches a crank angle detector for an engine includes a cam rotor platefor detecting a cylinder number to be ignited and a cam pulse sensorprovided opposite thereto, a crank rotor plate for sensing a crank angleand a crank pulse sensor provided opposite thereto, and a controller fordetermining ignition timings of respective cylinders to control anignition. The crank rotor plate is constituted by a rotor plate atstarting for sensing a fixed ignition timing and a rotor plate for anormal operation. A pair of crank pulse sensors are provided opposite tothe rotor plates, respectively. An input signal for the fixed ignitiontiming is mask-released only at starting. After that, input iscontinuously masked during normal operation.

European patent number DE 197 41 597, entitled CAM PULSE WHEEL FORINTERNAL COMBUSTION ENGINE, teaches The cam pulse wheel (14) is attachedto the camshaft with a variable phase and provided around its periphery(15) with a number of markings (16,17,18,19), corresponding to thenumber of engine cylinders, detected by a sensor (10), for determiningthe camshaft position. The markings are positioned asymmetrically, thesensor output signals fed to a microprocessor for adjustment of thecamshaft setting device.

As can be seen, it is known to use sensed pulse such as crank pulse todetermine parameters such as cylinder position. The above mentioned Andoapplication (2001/0011203) and Ando patent (U.S. Pat. No. 6,498,979)teaches a non-Variable Cam Timing system wherein a pulse missing portionof a series of crank pulses is referenced to cam signals by a computer.Magner patent (U.S. Pat. No. 5,736,633) teaches a system fordistinguishing a cylinder identification signal from a variable camtiming signal. In the Magner patent, the pulse wheel has separate teethor tabs for cylinder identification and variable cam timing. The tabsfor variable cam timing are physically spaced equidistance from eachother. Abe patent (U.S. Pat. No. 4,953,531) teaches relationship ofcrank and cam pulses with ignition pulses. In Abe, no variable camtiming relationships such as the controlled or adjusted angularrelationship between the crank and cam shafts is recited or described.However, the Yonezawa application (2002/0050272) specifically call for acylinder identifying system in associated with a variable valve timing(VVT) system in which the angular differences caused by the VVT systemare taken into consideration.

Pulse wheels or tooth wheels including asymmetrical pulse wheels areknown. German patent (DE 197 41 597) teaches an asymmetrical pulsewheel.

However, it is not known to use a given non-symmetrical pulse wheel ortooth wheel to accommodate existing VCT systems including at least onephaser in which a controller still considers pulse wheel as beingsymmetrical. Further, it is desirous to use the existing software andhardware for existing pulse wheel (usually a symmetrical pulse wheel) asmuch as possible on an asymmetrical pulse wheel in a VCT system havingat least one phaser and other devices. It is desirable to use a giventooth wheel with known dimensions including the non-symmetricalstructure along with exiting hardware and software. In other words, itis desirable to take the non-symmetrical structure into account and makethe computer or engine controller or other types of controllers to thinkthat the sensed pulses are still symmetrical. Thereby existing softwarewhich treats pulses as symmetrical can still be used.

It is also known that the performance of an internal combustion enginecan be improved by the use of dual camshafts, one to operate the intakevalves of the various cylinders of the engine and the other to operatethe exhaust valves. Typically, one of such camshafts is driven by thecrankshaft of the engine, through a sprocket and chain drive or a beltdrive, and the other of such camshafts is driven by the first, through asecond sprocket and chain drive or a second belt drive. Alternatively,both of the camshafts can be driven by a single crankshaft powered chaindrive or belt drive. Engine performance in an engine with dual camshaftscan be further improved, in terms of idle quality, fuel economy, reducedemissions or increased torque, by changing the positional relationshipof one of the camshafts, usually the camshaft which operates the intakevalves of the engine, relative to the other camshaft and relative to thecrankshaft, to thereby vary the timing of the engine in terms of theoperation of intake valves relative to its exhaust valves or in terms ofthe operation of its valves relative to the position of the crankshaft.

Consideration of information disclosed by the following U.S. patents,which are all hereby incorporated by reference, is useful when exploringthe background of the present invention.

U.S. Pat. No. 5,002,023 describes a VCT system within the field of theinvention in which the system hydraulics includes a pair of oppositelyacting hydraulic cylinders with appropriate hydraulic flow elements toselectively transfer hydraulic fluid from one of the cylinders to theother, or vice versa, to thereby advance or retard the circumferentialposition on of a camshaft relative to a crankshaft. The control systemutilizes a control valve in which the exhaustion of hydraulic fluid fromone or another of the oppositely acting cylinders is permitted by movinga spool within the valve one way or another from its centered or nullposition. The movement of the spool occurs in response to an increase ordecrease in control hydraulic pressure, P_(c), on one end of the spooland the relationship between the hydraulic force on such end and anoppositely direct mechanical force on the other end which results from acompression spring that acts thereon.

U.S. Pat. No. 5,107,804 describes an alternate type of VCT system withinthe field of the invention in which the system hydraulics include a vanehaving lobes within an enclosed housing which replace the oppositelyacting cylinders disclosed by the aforementioned U.S. Pat. No.5,002,023. The vane is oscillatable with respect to the housing, withappropriate hydraulic flow elements to transfer hydraulic fluid withinthe housing from one side of a lobe to the other, or vice versa, tothereby oscillate the vane with respect to the housing in one directionor the other, an action which is effective to advance or retard theposition of the camshaft relative to the crankshaft. The control systemof this VCT system is identical to that divulged in U.S. Pat. No.5,002,023, using the same type of spool valve responding to the sametype of forces acting thereon.

U.S. Pat. Nos. 5,172,659 and 5,184,578 both address the problems of theaforementioned types of VCT systems created by the attempt to balancethe hydraulic force exerted against one end of the spool and themechanical force exerted against the other end. The improved controlsystem disclosed in both U.S. Pat. Nos. 5,172,659 and 5,184,578 utilizeshydraulic force on both ends of the spool. The hydraulic force on oneend results from the directly applied hydraulic fluid from the engineoil gallery at full hydraulic pressure, P_(s). The hydraulic force onthe other end of the spool results from a hydraulic cylinder or otherforce multiplier which acts thereon in response to system hydraulicfluid at reduced pressure, P_(c), from a PWM solenoid. Because the forceat each of the opposed ends of the spool is hydraulic in origin, basedon the same hydraulic fluid, changes in pressure or viscosity of thehydraulic fluid will be self-negating, and will not affect the centeredor null position of the spool.

U.S. Pat. No. 5,289,805 provides an improved VCT method which utilizes ahydraulic PWM spool position control and an advanced control methodsuitable for computer implementation that yields a prescribed set pointtracking behavior with a high degree of robustness.

In U.S. Pat. No. 5,361,735, a camshaft has a vane secured to an end fornon-oscillating rotation. The camshaft also carries a timing belt drivenpulley which can rotate with the camshaft but which is oscillatable withrespect to the camshaft. The vane has opposed lobes which are receivedin opposed recesses, respectively, of the pulley. The camshaft tends tochange in reaction to torque pulses which it experiences during itsnormal operation and it is permitted to advance or retard by selectivelyblocking or permitting the flow of engine oil from the recesses bycontrolling the position of a spool within a valve body of a controlvalve in response to a signal from an engine control unit. The spool isurged in a given direction by rotary linear motion translating meanswhich is rotated by an electric motor, preferably of the stepper motortype.

U.S. Pat. No. 5,497,738 shows a control system which eliminates thehydraulic force on one end of a spool resulting from directly appliedhydraulic fluid from the engine oil gallery at full hydraulic pressure,P_(s), utilized by previous embodiments of the VCT system. The force onthe other end of the vented spool results from an electromechanicalactuator, preferably of the variable force solenoid type, which actsdirectly upon the vented spool in response to an electronic signalissued from an engine control unit (“ECU”) which monitors various engineparameters. The ECU receives signals from sensors corresponding tocamshaft and crankshaft positions and utilizes this information tocalculate a relative phase angle. A closed-loop feedback system whichcorrects for any phase angle error is preferably employed. The use of avariable force solenoid solves the problem of sluggish dynamic response.Such a device can be designed to be as fast as the mechanical responseof the spool valve, and certainly much faster than the conventional(fully hydraulic) differential pressure control system. The fasterresponse allows the use of increased closed-loop gain, making the systemless sensitive to component tolerances and operating environment.

U.S. Pat. No. 5,657,725 shows a control system which utilizes engine oilpressure for actuation. The system includes A camshaft has a vanesecured to an end thereof for non-oscillating rotation therewith. Thecamshaft also carries a housing which can rotate with the camshaft butwhich is oscillatable with the camshaft. The vane has opposed lobeswhich are received in opposed recesses, respectively, of the housing.The recesses have greater circumferential extent than the lobes topermit the vane and housing to oscillate with respect to one another,and thereby permit the camshaft to change in phase relative to acrankshaft. The camshaft tends to change direction in reaction to engineoil pressure and/or camshaft torque pulses which it experiences duringits normal operation, and it is permitted to either advance or retard byselectively blocking or permitting the flow of engine oil through thereturn lines from the recesses by controlling the position of a spoolwithin a spool valve body in response to a signal indicative of anengine operating condition from an engine control unit. The spool isselectively positioned by controlling hydraulic loads on its opposed endin response to a signal from an engine control unit. The vane can bebiased to an extreme position to provide a counteractive force to aunidirectionally acting frictional torque experienced by the camshaftduring rotation.

U.S. Pat. No. 6,247,434 shows a multi-position variable camshaft timingsystem actuated by engine oil. Within the system, a hub is secured to acamshaft for rotation synchronous with the camshaft, and a housingcircumscribes the hub and is rotatable with the hub and the camshaft andis further oscillatable with respect to the hub and the camshaft withina predetermined angle of rotation. Driving vanes are radially disposedwithin the housing and cooperate with an external surface on the hub,while driven vanes are radially disposed in the hub and cooperate withan internal surface of the housing. A locking device, reactive to oilpressure, prevents relative motion between the housing and the hub. Acontrolling device controls the oscillation of the housing relative tothe hub.

U.S. Pat. No. 6,250,265 shows a variable valve timing system withactuator locking for internal combustion engine. The system comprising avariable camshaft timing system comprising a camshaft with a vanesecured to the camshaft for rotation with the camshaft but not foroscillation with respect to the camshaft. The vane has acircumferentially extending plurality of lobes projecting radiallyoutwardly therefrom and is surrounded by an annular housing that has acorresponding plurality of recesses each of which receives one of thelobes and has a circumferential extent greater than the circumferentialextent of the lobe received therein to permit oscillation of the housingrelative to the vane and the camshaft while the housing rotates with thecamshaft and the vane. Oscillation of the housing relative to the vaneand the camshaft is actuated by pressurized engine oil in each of therecesses on opposed sides of the lobe therein, the oil pressure in suchrecess being preferably derived in part from a torque pulse in thecamshaft as it rotates during its operation. An annular locking plate ispositioned coaxially with the camshaft and the annular housing and ismoveable relative to the annular housing along a longitudinal centralaxis of the camshaft between a first position, where the locking plateengages the annular housing to prevent its circumferential movementrelative to the vane and a second position where circumferentialmovement of the annular housing relative to the vane is permitted. Thelocking plate is biased by a spring toward its first position and isurged away from its first position toward its second position by engineoil pressure, to which it is exposed by a passage leading through thecamshaft, when engine oil pressure is sufficiently high to overcome thespring biasing force, which is the only time when it is desired tochange the relative positions of the annular housing and the vane. Themovement of the locking plate is controlled by an engine electroniccontrol unit either through a closed loop control system or an open loopcontrol system.

U.S. Pat. No. 6,263,846 shows a control valve strategy for vane-typevariable camshaft timing system. The strategy involves an internalcombustion engine that includes a camshaft and hub secured to thecamshaft for rotation therewith, where a housing circumscribes the huband is rotatable with the hub and the camshaft, and is furtheroscillatable with respect to the hub and camshaft. Driving vanes areradially inwardly disposed in the housing and cooperate with the hub,while driven vanes are radially outwardly disposed in the hub tocooperate with the housing and also circumferentially alternate with thedriving vanes to define circumferentially alternating advance and retardchambers. A configuration for controlling the oscillation of the housingrelative to the hub includes an electronic engine control unit, and anadvancing control valve that is responsive to the electronic enginecontrol unit and that regulates engine oil pressure to and from theadvance chambers. A retarding control valve responsive to the electronicengine control unit regulates engine oil pressure to and from the retardchambers. An advancing passage communicates engine oil pressure betweenthe advancing control valve and the advance chambers, while a retardingpassage communicates engine oil pressure between the retarding controlvalve and the retard chambers.

U.S. Pat. No. 6,311,655 shows multi-position variable cam timing systemhaving a vane-mounted locking-piston device. An internal combustionengine having a camshaft and variable camshaft timing system, wherein arotor is secured to the camshaft and is rotatable but non-oscillatablewith respect to the camshaft is discribed. A housing circumscribes therotor, is rotatable with both the rotor and the camshaft, and is furtheroscillatable with respect to both the rotor and the camshaft between afully retarded position and a fully advanced position. A lockingconfiguration prevents relative motion between the rotor and thehousing, and is mounted within either the rotor or the housing, and isrespectively and releasably engageable with the other of either therotor and the housing in the fully retarded position, the fully advancedposition, and in positions therebetween. The locking device includes alocking piston having keys terminating one end thereof, and serrationsmounted opposite the keys on the locking piston for interlocking therotor to the housing. A controlling configuration controls oscillationof the rotor relative to the housing.

U.S. Pat. No. 6,374,787 shows a multi-position variable camshaft timingsystem actuated by engine oil pressure. A hub is secured to a camshaftfor rotation synchronous with the camshaft, and a housing circumscribesthe hub and is rotatable with the hub and the camshaft and is furtheroscillatable with respect to the hub and the camshaft within apredetermined angle of rotation. Driving vanes are radially disposedwithin the housing and cooperate with an external surface on the hub,while driven vanes are radially disposed in the hub and cooperate withan internal surface of the housing. A locking device, reactive to oilpressure, prevents relative motion between the housing and the hub. Acontrolling device controls the oscillation of the housing relative tothe hub.

U.S. Pat. No. 6,477,999 shows a camshaft that has a vane secured to anend thereof for non-oscillating rotation therewith. The camshaft alsocarries a sprocket that can rotate with the camshaft but is oscillatablewith respect to the camshaft. The vane has opposed lobes that arereceived in opposed recesses, respectively, of the sprocket. Therecesses have greater circumferential extent than the lobes to permitthe vane and sprocket to oscillate with respect to one another. Thecamshaft phase tends to change in reaction to pulses that it experiencesduring its normal operation, and it is permitted to change only in agiven direction, either to advance or retard, by selectively blocking orpermitting the flow of pressurized hydraulic fluid, preferably engineoil, from the recesses by controlling the position of a spool within avalve body of a control valve. The sprocket has a passage extendingtherethrough the passage extending parallel to and being spaced from alongitudinal axis of rotation of the camshaft. A pin is slidable withinthe passage and is resiliently urged by a spring to a position where afree end of the pin projects beyond the passage. The vane carries aplate with a pocket, which is aligned with the passage in apredetermined sprocket to camshaft orientation. The pocket receiveshydraulic fluid, and when the fluid pressure is at its normal operatinglevel, there will be sufficient pressure within the pocket to keep thefree end of the pin from entering the pocket. At low levels of hydraulicpressure, however, the free end of the pin will enter the pocket andlatch the camshaft and the sprocket together in a predeterminedorientation.

U.S. patent application Ser. No. 10/405,513, by inventors Earl EkdahlDanny R. Taylor and commonly assigned to BorgWarner Inc. of AuburnHills, Mich. teaches a method for compensating for variable cam timingof an internal combustion engine is provided. The method includes: a)providing a periodical crank pulse signal; b) providing a periodical campulse signal; c) determining a segment, wherein the internal combustionengine speed induces a volatile change upon Zphase values; d) dividingthe segment into sub-segments; and e) calculating Zphase values of aplurality of points within the sub-segments.

A typical prior art control loop is shown as follows. Referring to FIG.1, a prior art feedback loop 10 is shown. The control objective offeedback loop 10 is to have a spool valve in a null position. In otherwords, the objective is to have no fluid flowing between two fluidholding chambers of a phaser (not shown) such that the VCT mechanism atthe phase angle given by a set point 12 with the spool 14 stationary inits null position. This way, the VCT mechanism is at the correct phaseposition and the phase rate of change is zero. A control computerprogram product which utilizes the dynamic state of the VCT mechanism isused to accomplish the above state.

The VCT closed-loop control mechanism is achieved by measuring acamshaft phase shift θ₀ 16, and comparing the same to the desired setpoint 12. The VCT mechanism is in turn adjusted so that the phaserachieves a position which is determined by the set point 12. A controllaw 18 compares the set point 12 to the phase shift θ₀ 16. The comparedresult is used as a reference to issue commands to a solenoid 20 toposition the spool 14. This positioning of spool 14 occurs when thephase error (the difference between set point r 12 and phase shift 20)is non-zero.

The spool 14 is moved toward a first direction (e.g. right) if the phaseerror is negative (retard) and to a second direction (e.g. left) if thephase error is positive (advance). It is noted that the retarding withcurrent phase measurement scheme gives a larger value, and advancingyields a small value. When the phase error is zero, the VCT phase equalsthe set point 12 so the spool 14 is held in the null position such thatno fluid flows within the spool valve.

Camshaft and crankshaft measurement pulses in the VCT system aregenerated by camshaft and crankshaft pulse wheels 22 and 24,respectively. As the crankshaft (not shown) and camshaft (also notshown) rotate, wheels 22, 24 rotate along with them. The wheels 22, 24possess teeth which can be sensed and measured by sensors according tomeasurement pulses generated by the sensors. The measurement pulses aredetected by camshaft and crankshaft measurement pulse sensors 22 a and24 a, respectively. The sensed pulses are used by a phase measurementdevice 26. A measurement phase difference is then determined. The phasebetween a cam shaft and a crankshaft is defined as the time fromsuccessive crank-to-cam pulses, divided by the time for an entirerevolution and multiplied by 360.degree. The measured phase may beexpressed as θ₀ 16. This phase is then supplied to the control law 18for reaching the desired spool position.

A control law 18 of the closed-loop 10 is described in U.S. Pat. No.5,184,578 and is hereby incorporate herein by reference. Measured phase26 is subjected to the control law 18 initially wherein aProportional-Integral (PI) process occurs. PI process is the sum of twosub-processes. The first sub-process includes amplification; and thesecond sub-process includes integration. Measured phase is furthersubjected to phase compensation, where control signal is adjusted toincrease the overall control system stability before it is sent out todrive the actuator, in the instant case, a variable force solenoid.

As can be appreciated, in a VCT system having a controller forcontrolling phase relationship between two shafts based on angularinformation of shafts, there is need for the controller to treat sensedinformation in an orderly fashion.

SUMMARY OF THE INVENTION

In an Embedded Control System, a controller is provided to determine andadjust information derived from a tooth wheel having known teethdistributions.

In an Embedded Control System, a method is provided to determine andadjust information derived from a tooth wheel having known teethdistributions.

In an embedded VCT Control System, a controller is provided to determineand adjust information derived from a tooth wheel having known teethdistributions.

In an embedded VCT Control System, a method is provided to determine andadjust information derived from a tooth wheel having known teethdistributions.

Accordingly, in a VCT system having a phaser for adjusting an angularrelationship between a crank angle of the crank shaft and a cam angle ofa cam shaft, the system further has a controller adapted to determinethe angular relationship based on equally spaced teeth distributed uponthe circumference of at least one tooth wheel coupled to either thecrank shaft or the cam shaft, a method is provided. The method includesthe steps of: a) providing a tooth wheel having a physicallynon-symmetrical tooth distribution on the circumference of the wheel;and b) adjusting the physically non-symmetrical tooth distribution intoa symmetrical tooth distribution for further processing by thecontroller.

Accordingly, in a VCT device having a phaser for adjusting an angularrelationship between a crank angle of the crank shaft and a cam angle ofa cam shaft, the system further has a controller adapted to determinethe angular relationship based on equally spaced teeth distributed uponthe circumference of the crank shaft and the cam shaft respectively, amethod is provided. The method includes the steps of: providing a cranktooth wheel having known tooth distribution; providing a cam tooth wheelhaving known tooth distribution; and using the controller for adjustingvalues known to the controller as needed.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows a prior art control loop.

FIG. 1A shows a 3 tooth cam wheel.

FIG. 2 shows a set of pulse trains.

FIG. 3 shows a pulse wheel with equally spaced teeth FIG. 4 shows apulse wheel with asymmetrically spaced teeth FIG. 5 shows an adjustmentof an asymmetrical wheel.

FIG. 6 shows a schematic for recording a set of time stamps.

FIG. 7 shows a first flowchart depicting the present invention, in whicha crank wheel is non-symmetric, and a cam wheel is symmetric.

FIG. 8 shows a second flowchart depicting the present invention, inwhich a crank wheel is symmetric, and a cam wheel is non-symmetric.

FIG. 9 shows a third flowchart depicting the present invention, in whicha generic method suitable for a crank tooth wheel.

FIG. 10 shows a fourth flowchart depicting the present invention, inwhich a generic method suitable for a cam tooth wheel.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Phase Measurement Over 2 Crank Revolutions:

In an Embedded Control System, which are used primarily for control of aVCT system, pulse wheels are mounted on both the crankshaft and thecamshaft(s) of an internal combustion engine. These pulse wheels arechosen based on what sort of original equipment exists on the engine,what update rate is desired, and the basic relationship that existsbetween cam and crankshafts. This relationship may be such that forevery 2 revolutions of the crank, the cam revolves once. Therefore, inan arbitrary design of the present VCT system, a 4 pulse/rev wheel forthe crankshaft, and an 8 pulse/rev wheel for the camshaft(s) are chosen.Due to the relationship between the cam(s) and crank shafts, thefrequency of pulses from the pulse wheels is equal, i.e. at 4pulses/crank-revolution. Calibration and cam position measurement basedon this scheme are documented in U.S. Pat. Nos. 5,289,805 and 5,184,578,which are hereby incorporated herein by reference. Within thesedocuments, the cam position measurement scheme implicitly requires thereto be a relationship of twice the number of pulses on the camshaft pulsewheel, compared to the crankshaft pulse wheel. Further, the schemeimplicitly requires that there be an even number of camshaft teeth. Thisis a result of the 2:1 relationship. A counter example would be toarbitrarily pick 5 cam teeth (5 pulses/cam-revolution.), one would haveto have 2.5 teeth on the crankshaft. It is physically impossible to have½ of a tooth. Therefore, based on this current design, having oddnumbers of teeth on the cam pulse wheel is not practical.

A solution to the above problem or counter example is to count the crankteeth over two revolutions. When the crank teeth is counted over tworevolutions, the result is that instead of a 4/8 tooth combination, withthe 2:1 relationship, one can think of it as a 8/8, with a 1:1relationship.

Therefore, in a 3 tooth cam wheel, the 3 crank teeth wheel is countedover two revolutions, instead of 1½ teeth over just 1 crank revolutionsee FIG. 1A. Referring to FIG. 1A, a cam wheel 100 having three teeth100 a, 110 b, and 100 c is provided on the circumference of wheel 100.teeth 100 a, 110 b, and 100 c are evenly distributed upon thecircumference of wheel 100.

This case can be expended to the multiples of numeral 3. For example, a36-1 pulse/rev. crank wheel (36 evenly spaced teeth, with one missing,as an index) is used. Under normal operation, 4 tooth crank, 8 toothcam, one can count one tooth on the 36-1 wheel, skip 8 teeth, and countthe next one, etc. So, one counts every 9^(th) tooth, and come up with 4pulses/revolution. With the 3 tooth case, this also works, because over2 crank revolutions, one can get 72 pulses, which is evenly divided bythree. Therefore, one can count every 24^(th) tooth. As a result, thesoftware portions of a controller can start by counting tooth 5, andthen 29, both in the first revolution. To find the next tooth, one canadd 24 to that number, and find that:29+24=53

The next tooth ends up on the second crank revolution, so, bysubtracting 36 (the number of teeth in 1 whole revolution):53−36=17

It is found that the 3^(rd) tooth counted is the logical 17^(th), on the2^(nd) crank revolution. And figuring the next tooth(17+24)−36=5

Therefore, one ends right back where one started, i.e. at tooth 5. Onekeeps track of which crank revolution one is on by counting the index(which may be a missing tooth or an extra tooth or any designated toothon the wheel) tooth on the crank wheel. If it is odd, then it is crankrevolution 1, if it is even, it is crank revolution 2. See FIG. 2 for asimilar example with a 12 tooth crank wheel and a 3 tooth cam wheel.

Referring to FIG. 2, a set of pulse trains is shown. A crank pulse trainis provided on the top portion. Two revolutions of crank shaft areshown. The darkened pulses, i.e. pulses 2, 10, and 6 are theacknowledged teeth by the controller via a sensor. The non-darkenedpulses are the skipped teeth. In other words, for a twelve teeth crankwheel, only teeth 2 and 10 of the first revolution, and tooth 6 of thesecond revolution are acknowledged and counted.

Further, a cam pulse train having three pulses per cam revolution isprovided on the middle portion of FIG. 2. The three cam pulses are atthe same frequency as the three acknowledged pulses of the crank pulsetrain.

Due to the inherent dependency on counting the correct numbers of teeth,and the possibility of erroneous pulse events, one can add robustness tothis scheme by including an index tooth on the cam wheel. The index onthe crank serves to synchronize each single crank revolution, butbecause one counts over two revolutions, one may loose synchronizationfrom 1 revolution to another. However, since the cam turns ½ the speedof the crank, a once-per-rev index on the cams provides aonce-per-two-revolutions on the crank. So, by simply using a 3+1 camtooth wheel, this arrangement of counting teeth over two crankrevolutions is sufficiently robust and versatile.

Non-Symmetrical Tooth Spacing—Concept:

Using tooth wheels with equally spaced teeth is probably the moststraightforward way of speed and phase measurement of a rotating system(FIG. 3). Referring to FIG. 3, a tooth wheel 200 having four equallyspaced teeth 200 a, 200 b, 200 c, and 200 d is provided on thecircumference of wheel 200.

However, on occasion, the tooth wheels will have tooth spacing that isinconsistent or asymmetrical. This is also referred to asNon-Symmetrical Tooth Spacing (FIG. 4). Referring to FIG. 4, anasymmetrical tooth wheel 300 is shown. Wheel 300 has four teeth on thecircumference thereon. Tooth 300 a is space 60 degrees from tooth 300 band 120 degrees from tooth 300 d. Tooth 300 b is spaced 60 degrees fromtooth 300 c, which is spaced 120 degrees from tooth 300 d.

This invention requires a 2:1 ratio of cam to crank teeth. If a singlecrank revolution is insufficient for measurement purposes, the: PhaseMeasurement over 2 Crank revolutions described supra can be used. It isnoted that this concept is an enhancement to the basic VCT cam positionmeasurement method described in U.S. Pat. No. 5,289,805,Self-Calibrating Variable Camshaft Timing System. The basic equationstated within is:${{camposition}({phase})} = {\frac{{cam}_{timelagfromcrankpulse}}{timebetweencrankpulses} \times \frac{360\quad{degrees}}{N}}$

-   -   (1)        where N is the number of evenly spaced teeth on the tooth wheel.        The right side of the equation divides N into 360, which denotes        degrees between teeth that is at consistent degree spacing. This        spacing is used to scale the left side of the equation so that        it represents a cam position (phase), in degrees relative to the        crank. This equation works very well for phase measurement, and        is extremely robust. Robust is defined as a condition wherein        erroneous information are less likely to cause a fault. Robust        also denotes simplicity in that a routine is easy to implement,        and thus, more likely to be implemented in software without        coding errors. Complex routines are harder to test and verify        working in software.

The present invention teaches a Non-Symmetric tooth spacing using thissame equation, and only modifies the parameters that the equation uses.In other words, exiting controller method can still be used. During thepulse-interrupt routines, an adjustment to the measured parameters isperformed, in which a Non-symmetric tooth wheel is transformed in theeyes of the controller to look symmetric. For example, if there are 5teeth on the pulse-wheel, it will adjust the measured numbers such thatit represents 360/5=72 degrees between the required teeth.

Starting with known spacing between the teeth on a pulse-wheel, thedegree change from each tooth location may be determined; such that thephysical asymmetrical teeth distribution can be transformed or adjustedto symmetrical tooth spacing as far as the controller is concerned.Using our 5-tooth wheel as an example, if the first tooth was at 50degrees, our change would be +22 degrees, placing it at 72 degrees. Ifour next tooth was at 150 degrees, our change would be −6 degrees,bringing it back to 144 degrees, and so on. Since the processoracknowledges each tooth by capturing the system time, one need to make acorrelation from time between pulses to a change in degrees.

Crank Non-Symmetric, Cam Symmetric

Working from equation (1), one will refer to time between crank pulsesas CrankPeriod. This is calculated as follows:CrankPeriod=TC−CrankTimeStamp  (2)

Where TC is the Timer Capture triggered by the crank pulse, andCrankTimeStamp is the Timer Capture recorded on the previous crankpulse. Right after this equation, one need to update the CrankTimeStamp,which is simply:CrankTimeStamp=TC  (3)

The system time when the last cam pulse occurred will be referred to asTC(timer capture). In equation (1):time lag from crank pulse (CamTimeLag)=TC−CrankTimeStamp  (4)

One other association to make is the right side of equation (1), whichworks out to be the degree spacing between teeth in N number of evenlyspaced teeth.Even _(—) tooth _(—) spacing=360 degrees/N number of teeth  (5)

Equation (5) can be calculated in advance, and does not change in agiven pulse-wheel configuration. Equations (2-4) are executed in theorder they are presented. So far, there is nothing new about theequations that have been mentioned. Equation (1) is used like itnormally used. To adapt to the present invention, equation (2) isexecuted normally. Since this equation will not give a correct valuewith a non-symmetric pulse-wheel, another equation is required to adjustthe tooth spacing to mimic an evenly spaced pulse-wheel. $\begin{matrix}{{CrankPeriod}_{adj} = {\frac{{Even\_ tooth}{\_ spacing}}{\deg.{spacingofcurrentgap}} \times {CrankPeriod}}} & (6)\end{matrix}$

CrankPeriod_(adj) is a newly adjusted value. Instead of using equation(3), one substitute it for this equation:CrankTimeStamp _(adj) =CrankPeriod _(adj) +CrankTimeStamp  (7)

It is important to clarify that CrankTimeStamp_(adj) is the correctvalue for the current pulse, but CrankTimeStamp is actually from theprevious pulse calculations. In this fashion, CrankTimeStamp_(adj) willbe the CrankTimeStamp for the next time one execute these equations.Both of these equations which adjust the readings to represent an evenlyspaced tooth wheel are executed in the crank pulse-wheel interruptroutine in the software. This takes place immediately after themeasurement of CrankPeriod (FIG. 5).

Referring to FIG. 5, an exemplified adjustment of an asymmetrical wheel400 is shown. The distribution of the teeth thereon can be considered asanalogous to that of FIG. 4. Wheel 400 possesses four asymmetricallydistributed teeth. The 4 teeth are tooth 401, tooth 402, tooth 403, andtooth 404. Wheel 400 rotates clockwise and the asymmetricallydistributed teeth thereon is sensed by sensor 405. as can be seen, tooth401 fits the correct spacing or the evenly distributed tooth space.Therefore, no adjustment is required.

For tooth 402, a backward or counter clockwise movement of 30 degreessuch that tooth 402 is at 90 degrees angular distance from both tooth401 and tooth 403 is accomplished. One can designate the imaginary ornon-physical tooth 402′. Tooth 402′ is imaginary in that a controllersuch as an engine control unit (ECU) of an internal combustion enginemay be taught to think that teeth on wheel 400 is still evenly orsymmetrically distributed due the location of the imaginary ornon-physical tooth 402′.

Similar to tooth 401, and since tooth 403 is 180 degrees from tooth 401,it fits the correct spacing and is not adjusted. Further, with regard totooth 404, similar to tooth 402 it is adjusted or moved forward orclockwise 30 degrees so that it lies 90 degrees to its adjacent teeth.

Assuming the angular relationship as shown in FIG. 5 and assuming wheel400 is a crank wheel, one arrives at the following:

For tooth 1: no adjustment required; Tooth  2:${CrankPeriod}_{1{–2}^{\prime}} = {\frac{90{{^\circ}({evenspacing})}}{60{{^\circ}({currentspacing})}}*{CrankPeriod}_{1{–2}}}$ CrankTimeStamp _(2′) =crankPeriod _(1-2′) +CrankTimeStamp ₁

Tooth 3: no adjustment required since it lies 180 degrees from tooth 1.Tooth  4:${CrankPeriod}_{3{–4}^{\prime}} = {\frac{90{{^\circ}({evenspacing})}}{120{{^\circ}({currentspacing})}}*{CrankPeriod}_{3{–4}}}$ CrankTimeStamp _(4′) =crankPeriod _(3-4′) +CrankTimeStamp ₃

Note that the calculation of CrankPeriod₁₋₂ & CrankPeriod₃₋₄ is notshown, but is implied through equation (2).

There also needs to perform some additional operations in each of thecam pulse-wheel interrupt routines. The normal equation in the caminterrupt routines is:CamTimeLag=TC(current system timer capture)−CrankTimeStamp  (8)

This is used in this configuration as is, but the CrankTimeStamp is thenew adjusted value. However, additional checks are made based on theresults of this equation:

If (CamTimeLag<0)CamTimeLag _(adj) =CamTimeLag+CrankPeriod _(adj)  (9)

If (CamTimeLag>CrankPeriod_(adj))CamTimeLag _(adj) =CamTimeLag−CrankPeriod _(adj)

These checks will account for an adjusted crank tooth which either movesin front of, or behind the time in which the cam tooth is measured.Since the CamTimeLag is a measure of the current time (in a caminterrupt routine) back to when the last crank pulse occurred, if thecrank pulse is adjusted to occur later in time, the calculations willnot represent the correct phase unless adjusted based on the condition.Also, if after equation (8) one do not meet the need to be adjusted,based on the checks in (9), then one will use the non-adjustedCamTimeLag measurement. Otherwise, one will use the adjusted value inour cam position (phase) measurement equation, (1).

Referring to FIG. 6, a cam wheel 500 is provided in which a set of teeth502 (only four shown) is distributed on the circumference of wheel 500.The set of teeth 502 may be symmetrically or asymmetrically distributed.A sensor 504 is disposed to sense each tooth and create a correspondingpulse for a controller to record a cam time stamp therein. As can beappreciated, the controller is capable of recording a first valuetherein corresponding to a first pulse, and a second value thereincorresponding to a second pulse. The timing between pulses can berecorded by the controller for controlling purposes.

Similarly, a crank wheel 506 is provided in which a set of teeth 508(only four shown) is distributed on the circumference of wheel 506. Theset of teeth 508 may be symmetrically or asymmetrically distributed. Asensor 510 is disposed to sense each tooth and create a correspondingpulse for a controller to record a crank time stamp therein. As can beappreciated, the controller is capable of recording a first valuetherein corresponding to a first pulse, and a second value thereincorresponding to a second pulse. The timing between pulses can berecorded by the controller for controlling purposes.

The cam time stamp and crank time stamp are used by the controller 512for use and control by the controller 512. Controller 512 may be anytype of controller including an Engine Control Unit (ECU) of an internalcombustion engine. Time stamp is a measured value. By way of an example:when a pulse arrives at the processor of controller from a sensor, theInterrupt routine looks at the system clock, and records the time.

Referring to FIG. 7, a flowchart 700 depicting a physical layout whereinthe crank shaft has a non-symmetric tooth wheel and the cam shaft has asymmetric tooth wheel. An interrupt is initially generated for at thestart of the flow. Crank period is set as the difference between TC andthe measured crank time stamp (Step 704). TC denotes the timer capture,which mathematically presents the same thing as the time stamp. In theorder of things, when the sensor is excited by the passing tooth, theinterrupt hardware/software in the controller captures the system timein a system register (variable). This process is termed the TimerCapture. For example, the above mentioned hardware may execute theinterrupt routine, and then the timer capture value is copied to theTimestamp variable. Instead of using Timer Capture for the calculations,the present invention uses a separate variable, which is robust insoftware design, wherein TC (just received)—Timestamp (from last time)is executed right before we manually copy TC over to Timestamp. Theadjusted crank period is set as equal to the even tooth spacing of thecurrent gap in degrees. Even tooth spacing is defined as 360 degreesdivided by the total number of teeth on a sensor wheel. Current gap isdefined as spacing, in degrees, between teeth in the real physicalrelationship, i.e. not adjusted by the controller. The quotient in turnis multiplied by crank period value (Step 706). Crank time stamp is setas the sum of the adjusted crank time period and the crank time stamp(Step 708). As can be appreciated, due to the asymmetric nature of thecrank wheel, and the fact that the asymmetric distribution of the teethis know, an adjust can be done to reflect or make the controller awareof the non-symmetric distribution and still using the system clock withthe same level of accuracy by spacing the tooth signal apart just as wasdone when the teeth are physically apart.

At this juncture, a first determination is performed (Step 710), if camtime lag value is less than zero, the adjusted cam time lag value is setas the summation of the known cam time lag and the adjusted crank period(Step 712). The subroutine is done and flow reverts back toward phasemeasurement (Step 714). Cam Time Lag is defined as the time differencefrom latest cam timestamp to the latest crank timestamp. As this timedifference changes, this represents the change in phase between thecrank and cam. One can either measure from crank to cam, or cam to crank(in this case, we arbitrarily use cam to crank), the only difference isthe sign of the number.

However, if cam time lag is less than zero, a second determination (Step716) is performed. The second determination determines whether cam timelag is greater than the adjusted crank period (Step 716). If cam timelag is greater than the adjusted crank period, the adjusted cam time lagis set as the difference of cam time lag and the adjusted crank period(Step 718). If cam time lag is less than the adjusted crank period, theflowchart 700 flows toward the phase measurement (Step 714).

Crank Symmetric, Cam Non-Symmetric

In this case, the crank pulse-wheel interrupt routine is unchanged. Thecalculations of CrankPeriod and CrankTimeStamp are executed as normal:CrankPeriod=TC−CrankTimeStamp //Current system time−last time  (10)CrankTimeStamp=TC //Update system time  (11)

One may note that equations (10 &11) are the same as equations (2 & 3).For the case of the cam pulse-wheel interrupt routine, there is areplacement of the previous equation (8), plus it also incorporates thechecks that are shown above (9). $\begin{matrix}\begin{matrix}{{*{CamTL}} = {{TC} - {*{CrankTS}} -}} \\{\left\{ {\frac{Current\_ spacing}{{Even\_ tooth}{\_ spacing}} - 1} \right\} \times {CrankPeriod}}\end{matrix} & (12)\end{matrix}$

*CamTL and *CrankTS are abbreviations of CamTimeLag and CrankTimeStamp,respectively.

The calculation checking that one incorporate is similar to the abovecase.

If (CamTimeLag<0)CamTimeLag _(adj) =CamTimeLag+CrankPeriod _(adj)  (13)

If (CAMT0>CrankPeriod_(adj))CamTimeLag _(adj) =CamTimeLag−CrankPeriod _(adj)

Referring to FIG. 8, a flowchart 800 depicting a physical layout whereinthe crank shaft has a symmetric tooth wheel and the cam shaft has anon-symmetric tooth wheel. An interrupt is initially generated for atthe start of the flow. Crank period is set as the difference between TCand the measured crank time stamp (Step 804). Crank time stamp is set asTC (Step 806). Cam time lag is set as the difference between TC andCrank time stamp and the relative adjustment of tooth spacing depictedin time. In other words, Cam time lag equals TC minus crank time stampminus the quotient or the ratio of the current spacing (the actualphysical layout on the tooth wheel) and the desired even tooth spacingfor the controller to recognize and process. The ratio is in turnmultiplied by the crank period.

At this juncture, a first determination is performed (Step 810), if camtime lag value is greater than zero, the adjusted cam time lag value isset as the summation of the known cam time lag and the adjusted crankperiod (Step 812). The subroutine is done and flow reverts back towardphase measurement (Step 814). However, if cam time lag is less thanzero, a second determination (Step 816) is performed. The seconddetermination determines whether cam time lag is greater than theadjusted crank period (Step 816). If cam time lag is greater than theadjusted crank period, the adjusted cam time lag is set as thedifference of cam time lag and the adjusted crank period (Step 818). Ifcam time lag is less than the adjusted crank period, the flowchart 800flows toward the phase measurement (Step 814).

Crank Non-Symmetric, Cam Non-Symmetric

In the case where both the crankshaft and camshafts have Non-symmetrictooth spacing, one would use both sets of “adjustment” equations listedabove to have both the crank and cams appears as evenly spaced teeth. Inother words, both a crank interrupt and a cam interrupt are performed,in which FIGS. 9 and 10 describe respectively.

Referring to FIG. 9, a flow chart 900 depicting a crank pulse interruptis depicted. A controller initiates crank pulse interrupt 902 and crankpulse interrupt starts. Crank period is set as the difference between TCand crank time stamp (Step 904). At this juncture, a determination as towhether the current spacing of crank pulse wheel is symmetric isperformed (Step 904). It is noted that typically the shape of a toothwheel is known in that the controller can set or reset to reflect thefact or the actual physical shape of the tooth wheel. If the currentspacing is symmetric, the crank time stamp is set as equal to TC (Step908). The interrupt subroutine ends (Step 910). However, If the currentspacing is non-symmetric, the crank period needs to be adjusted for thecontroller. The adjusted crank period is set to be equal to the productof a ratio multiplied by crank period. The ratio reflects thenon-symmetrical tooth distribution on the tooth wheel and mathematicallyequal to even tooth spacing divided by the current gap between therelevant adjacent teeth in degrees or radius (Step 912). At thisjuncture, Crank time stamp needs to be adjusted as well. The adjustedcrank time stamp is set as the summation of the adjusted crank periodand the crank time tamp known the controller up to this point (Step914). The non-symmetric nature of the crank pulse wheel being thusreflected, the routine ends (910).

Referring to FIG. 10, a flow chart 1000 depicting a cam pulse interruptis depicted. A controller initiates cam pulse interrupt 1002 and campulse interrupt subroutine starts. At this juncture, a firstdetermination is performed as to whether the current cam wheel issymmetric (Step 1004). If the cam wheel is symmetric, the cam time lagis set as the difference between TC and crank time stamp (Step 1006). Ifthe cam wheel is non-symmetric, the cam time lag is set as thedifference of TC minus crank time stamp and minus the product of afactor and crank period. The factor is defined as a ratio minus one, inwhich the ratio is the ratio of the current spacing (uneven) and theeven tooth spacing of the controller (Step 1008). At this juncture, asecond determination is performed as to whether the cam time lag valueis less than zero (Step 1010). If the cam time lag value is less thanzero, the cam time lag needs to be adjusted. The adjusted cam time lagis set as the summation of cam time lag (currently known) and thecurrently known adjusted crank period (Step 1012). If the cam time lagvalue is not less than zero, a third determination is performed as towhether cam time lag is greater than the adjusted crank period (Step1014). If cam time lag is greater than the adjusted crank period, theadjusted cam time lag is set as the known cam time lag plus the adjustedcrank period (Step 1016). If cam time lag is not greater than theadjusted crank period, the crank time stamp value is set as the currentTC value (Step 1018).

This invention requires there be twice the number of teeth on thecamshaft, such that the frequencies of pulses entering the controllerare the same. To enable this invention with a number of teeth that doesnot follow this rule, one may need to incorporate this with two otherconcepts, Tooth Skipping and Phase Measurement over 2 crank revolutionsas discussed supra.

It is very important to keep track of which tooth one is counting. Onealways needs to know what tooth is being counted, and what size spaceoccurs from one tooth to the next. In this scheme, if there were onlyslight variation between tooth spacing, it would be advantageous toinclude a unique index tooth, which can be easily identified and used tore-synchronize the tooth count.

One embodiment of the invention is implemented as a program product foruse with a computer system such as, for example, the schematics shown inFIG. 6 and described below. The program(s) of the program productdefines functions of the embodiments (including the methods describedbelow with reference to FIGS. 7-10 and can be contained on a variety ofsignal-bearing media. Illustrative signal-bearing media include, but arenot limited to: (i) information permanently stored on in-circuitprogrammable devices like PROM, EPPOM, etc; (ii) information permanentlystored on non-writable storage media (e.g., read-only memory deviceswithin a computer such as CD-ROM disks readable by a CD-ROM drive);(iii) alterable information stored on writable storage media (e.g.,floppy disks within a diskette drive or hard-disk drive); (iv)information conveyed to a computer by a communications medium, such asthrough a computer or telephone network, including wirelesscommunications, or a vehicle controller of an automobile. Someembodiment specifically includes information downloaded from theInternet and other networks. Such signal-bearing media, when carryingcomputer-readable instructions that direct the functions of the presentinvention, represent embodiments of the present invention.

In general, the routines executed to implement the embodiments of theinvention, whether implemented as part of an operating system or aspecific application, component, program, module, object, or sequence ofinstructions may be referred to herein as a “program”. The computerprogram typically is comprised of a multitude of instructions that willbe translated by the native computer into a machine-readable format andhence executable instructions. Also, programs are comprised of variablesand data structures that either reside locally to the program or arefound in memory or on storage devices. In addition, various programsdescribed hereinafter may be identified based upon the application forwhich they are implemented in a specific embodiment of the invention.However, it should be appreciated that any particular programnomenclature that follows is used merely for convenience, and thus theinvention should not be limited to use solely in any specificapplication identified and/or implied by such nomenclature.

Accordingly, it is to be understood that the embodiments of theinvention herein described are merely illustrative of the application ofthe principles of the invention. Reference herein to details of theillustrated embodiments are not intended to limit the scope of theclaims, which themselves recite those features regarded as essential tothe invention.

1. In a VCT system having a phaser for adjusting an angular relationship between a crank angle of the crank shaft and a cam angle of a cam shaft, the system further has a controller adapted to determine the angular relationship based on equally spaced teeth distributed upon the circumference of at least one tooth wheel coupled to either the crank shaft or the cam shaft, a method comprising the steps of: a) providing a tooth wheel having a physically non-symmetrical tooth distribution on the circumference of the wheel; and b) adjusting the physically non-symmetrical tooth distribution into a symmetrical tooth distribution for further processing by the controller.
 2. In a VCT device having a phaser for adjusting an angular relationship between a crank angle of the crank shaft and a cam angle of a cam shaft, the system further has a controller adapted to determine the angular relationship based on equally spaced teeth distributed upon the circumference of the crank shaft and the cam shaft respectively, a method comprising the steps of: providing a crank tooth wheel having known tooth distribution; providing a cam tooth wheel having known tooth distribution; and using the controller for adjusting values known to the controller as needed.
 3. The device of claim 2, wherein the using step comprises running a cam pulse interrupt subroutine for determining a first set of adjusted values.
 4. The device of claim 2, wherein the using step comprises running a crank pulse interrupt subroutine for determining a second set of adjusted values.
 5. The device of claim 2, wherein the crank tooth wheel having known tooth distribution comprises symmetric tooth distribution.
 6. The device of claim 2, wherein the crank tooth wheel having known tooth distribution comprises non-symmetric tooth distribution.
 7. The device of claim 2, wherein the cam tooth wheel having known tooth distribution comprises symmetric tooth distribution.
 8. The device of claim 2, wherein the cam tooth wheel having known tooth distribution comprises non-symmetric tooth distribution. 